In a liquid crystal display device or an organic light-emitting diode (OLED) display device and the like, an array substrate is one of the important components. The array substrate includes a plurality of thin film transistors; each thin film transistor mainly includes a gate, an active layer, a source and a drain, wherein a gate insulating layer is arranged between the gate and the active layer. In addition, each thin film transistor may further include other insulating layers such as an inter-level dielectric (ILD) layer and the like between the source/drain and the active layer.
In the thin film transistor of the existing array substrate, the gate insulating layer is made of silicon oxide or silicon nitride of which the dielectric constant is relatively low and is about 3.9-7.9. Thus, the gate insulating layer is relatively thick (about 140-240 nm) in order to achieve enough insulation performance and storage capacitance, which is unfavorable for the miniaturization of the thin film transistor and hinders the improvement on the resolution of a display device. Moreover, the contact face between the gate and the gate insulating layer has many defects due to a great lattice constant difference between the materials of the gate and the gate insulating layer, so the gate insulating layer is also required to be relatively thick in order to make the lattices of the two to match with each other.